Lambda the Ultimate

As a long-time developer, I've created more bugs than is even remotely funny, so I'm not trying to make this a complaint or a witch hunt. Rather, I would really like to know how realistic it is to avoid bugs in the 'fundamentals' (relative term) of a programming language, and still have a language that is use/able in the real world? Testing & Modeling are the answer, I assume, but who has really applied them rigorously in the development of a programming language? It scares me that the tools we're supposed to build on might not be hallowed ground from a quality standpoint. (Yes, I know there are good reasons to trade off quality vs. speed.) I feel like there's something about "obviously no bugs" vs. "no obvious bugs" here, mixed in with issues of how the programming language will affect the program language; the simpler the programming language, the more we're just shifting the bugs out to all of the programs?

Often in modularity discussions the concept of "local reasoning" is discussed, and it's always assumed we want to make it easier, as a tactic for in turn making it easier for programmers to keep programs in their head. 'Local' to me implies that we have some notion of distance, and I'm curious what work if any has been done on measuring that distance. I've seen lots of claims about X or Y language feature reducing the ability to engage in local reasoning, but no attempts at quantification, without which I don't understand how the languages can be properly compared. Papers, links to prior discussions, etc. appreciated.